The overall objectives of this research program continue to be the investigation of the regulation of the coordinated expression of non-linked genes during the course of differentiation of eukaryotic cells. The system employed in these studies has been the Friend virus complex infected murine erythroleukemia cell (MELC). In the original application submitted for the period beginning 7/1/79, details of the extensive characterization of the system provided by studies in our laboratory as well as by a number of other investigators were provided. During the past year, the program of research made progress in studies on: 1) relationship between cell division cycle and induced differentiation; 2) studies on DNA replication and on the replication of erythropoiesis specific gene sequences during induced differentiation; 3) globin mRNA accumulation during induced differentiation; 4) studies on the effects of tumor promoters on MELC and normal hematopoietic cell differentiation; and 5) gene structure in erythroleukemic cells.